Atrio-Ventricular Septal Defect

The Rastelli classification of atrioventricular septal defect (AVSD) categorizes the anatomy of the common AV valve based on how the chordal attachments of the valve relate to the ventricular septum. This classification is important for surgical planning and determining the complexity of repair.

Rastelli Types of AVSD:

1. Type A (Most Common)

   • The superior bridging leaflet is split at the level of the ventricular septum.

   • The left superior (anterior) leaflet (LSL) remains entirely within the left ventricle, while the right superior (anterior) leaflet (RSL) is positioned exclusively within the right ventricle.

2. Type B (Rare)

   • The superior bridging leaflet is divided and attaches to a papillary muscle in the right ventricle.

   • The abnormal papillary muscle attachment originating from the right side of the ventricular septum connects to the left portion of the common superior (anterior) bridging leaflet.

   • This type is extremely rare and is often associated with heterotaxy syndromes.

   • Surgical repair can be more complex due to abnormal chordal distribution.

3. Type C - Click here for example

   • The superior bridging leaflet remains intact and free-floating, without septal attachment. This type features significant bridging of the ventricular septum by the superior (anterior) bridging leaflet (SL), which remains intact and does not divide. It is free-floating without any chordal attachments to the septal crest. The posterior common leaflet may either be divided or undivided, but in most cases, it is well anchored.

   • This leads to a large communication between the left and right ventricles.

   • Surgical correction is more challenging, requiring careful reconstruction of the left AV valve to ensure competent function.

Partial AVSD

• Primum ASD: This defect is located in the lower atrial septum, just anterior to the coronary sinus orifice. A key echocardiographic feature is that the atrioventricular (AV) valves attach to the interventricular septum (IVS) at the same level. As with all atrial septal defects, assessing the degree of right ventricular volume overload (RVVO) is essential.

• Cleft Mitral Valve: In partial AVSD, the anterior mitral leaflet has a cleft, with chordal attachments extending to the IVS. These attachments can contribute to left ventricular outflow tract obstruction (LVOTO). Imaging should focus on the degree and location of mitral regurgitation (MR), the chordal anatomy, and evaluating for any LVOTO.

Complete AVSD

• Balanced AVSD: This condition involves both an atrial and ventricular septal defect (VSD). The term "balanced" refers to the relative size of the ventricles, particularly the inlet portion (determined by the size of the AV valves). Given that AVSDs are often part of complex congenital heart disease, it is crucial to evaluate systemic and venous return. Additional anomalies to assess include:

  • Presence of additional VSDs.

  • Patent ductus arteriosus (PDA).

  • AV valve regurgitation, with attention to the origin of the regurgitant jet.

  • AV valve morphology, classified using the Rastelli system (Types A, B, and C), best assessed in an en face subcostal view (between coronal and sagittal planes at the level of the AV valve leaflet tips).

• Unbalanced AVSD: In this variation, one ventricle is significantly larger than the other. Evaluating the inlet (AV valve size) of each ventricle is especially important. Unbalanced AVSDs are frequently associated with heterotaxy, making it essential to assess abdominal situs and systemic and venous return patterns. If the stomach is located on the opposite side of the cardiac apex, heterotaxy is likely present. Additionally, the great vessel supplied by the smaller ventricle may develop stenosis; for example, if the left-sided structures are hypoplastic, there may be a risk of coarctation of the aorta.

Chordal Attachments

• Evaluate for straddling, where one side of an AV valve is attached to the opposite ventricle.

• Assess for override, where blood flow from one side of an AV valve enters the other ventricle.

AV Valve Morphology

• In complete and balanced AVSD, it is crucial to define the atrioventricular valve (AVV) anatomy using an en face subcostal view (between the coronal and sagittal planes at the level of the AV valve leaflet tips).

• AV valve anatomy is classified using the Rastelli system, based on the characteristics of the anterosuperior bridging leaflet.

  • Rastelli Type A (“Attached”) – The anterior and anterolateral bridging leaflets are equal in size and attach medially to the crest of the interventricular septum (IVS).

  • Rastelli Type B (“Bridge”) – The anterior bridging leaflet is partially divided and does not attach to the IVS. Instead, it connects to a right ventricular papillary muscle arising from the RV septal surface (associated with a short moderator band).

  • Rastelli Type C (“Cut”) – The anterolateral leaflet is small and displaced toward the right side, while the anterior bridging leaflet appears to "float" above the IVS.

• Important Note: This classification should not be attempted from an apical four-chamber view.

Physiological Impact of AVSD

• In the absence of pulmonary stenosis (PS), an atrioventricular septal defect results in left-to-right shunting at both the atrial and ventricular levels.

• The ventricular septal defect (VSD) is large, leading to equalized right and left ventricular pressures and elevated pulmonary artery pressures (PAH).

• Once pulmonary vascular resistance drops, there is increased pulmonary blood flow, resulting in pulmonary overcirculation and congestive heart failure.

• The physiological impact varies depending on the complexity of the AVSD and associated anomalies.

Echocardiographic for AVSD Assessment

1. Imaging the AV Canal

• Define AV valve morphology and attachments.

• Assess AV valve balance, including commitment of the AV valve to each ventricle and ventricular size.

  • Use the subcostal "in-between" en face view (~4:30 pm notch position).

• Evaluate for AV valve insufficiency and determine the mechanism of regurgitation.

• Assess the subvalvular apparatus, with a focus on papillary muscle anatomy, particularly in cases where closing the cleft mitral valve might cause mitral stenosis.

• Obtain an en face view of the AV valve.

2. Hemodynamic Assessment

• Assess the global cardiac function and impact of volume and pressure overload on both ventricles.

• Evaluate left ventricular systolic function:

  • M-mode fractional shortening (FS) and biplane ejection fraction (EF) using Simpson’s rule.

• Measure left atrial (LA) size using the LA/AO ratio in the parasternal short-axis (PSSA) view.

  • LA/AO ratio >1.6 suggests a significant left-to-right shunt.

• Assess left ventricular (LV) size using:

  • M-mode LV end-diastolic dimension (LVEDd) Z-score.

  • LV end-diastolic volume (LVEDV) via biplane EF measurement.

• Estimate pulmonary artery (PA) pressure:

  • Measure the pressure gradient between LV and RV using Doppler assessment of VSD flow velocity (use best-aligned Doppler signal).

  • Estimate PA pressure via peak TR velocity (for RV and PA systolic pressures) and peak PR velocity (for mean PA pressure assessment).

Detection of Associated Lesions

• Left Ventricular Outflow Tract Obstruction (LVOTO)

  • In complete AV canal defects (CAVC), the LVOT is elongated and narrowed, resulting in a gooseneck deformity on angiography.

  • The aortic valve remains in its normal position, but the bridging leaflets create a shallow LVOT, increasing obstruction risk.

  • Potential causes of LVOTO:

    • Accessory left-sided AV valve attachments to the septum (more common in Rastelli Type A).

    • Discrete subaortic membrane formation.

    • Anomalous or prominent anterolateral papillary muscle.

• Right Ventricular Outflow Tract Obstruction (RVOTO) – Evaluate for Tetralogy of Fallot (TOF).

• Patent Ductus Arteriosus (PDA) – If PA pressures are systemic, the PDA may be difficult to detect.

• Aortic Arch Anomalies – Assess for coarctation, especially in RV-dominant CAVC.

• Septal Defects – Evaluate the atrial and ventricular septum for additional defects.

• Systemic and Pulmonary Venous Connections

  • Assess for left superior vena cava (L-SVC) and partial anomalous pulmonary venous return.

  • Rule out coronary sinus septal defect.

Postoperative Assessment

• Residual Septal Defects

  • Evaluate for any residual atrial or ventricular septal defects, particularly in early postoperative studies.

• Tricuspid Valve Assessment

  • Check for tricuspid stenosis from apical views using pulsed and CW Doppler.

  • Assess tricuspid regurgitation from apical and parasternal long-axis views.

  • Estimate right ventricular pressure using TR jets (from apical and parasternal views).

• Mitral Valve Evaluation

  • Assess for mitral stenosis and regurgitation; if stenosis is present, measure the mean inflow gradient.

  • Perform an en-face parasternal short-axis assessment of the mitral valve to determine the mechanism of regurgitation (e.g., residual cleft).

  • Use color Doppler and 2D imaging side-by-side. Consider 3D imaging for a detailed mitral valve assessment.

• Subaortic Region Evaluation

  • Assess for subaortic obstruction using imaging, pulsed Doppler, and color Doppler.

• Aortic Valve Function

  • Evaluate for aortic regurgitation.

Presentation by Elissa Remmer and Stephanie Mardakis on Atrio-Ventricular Septal Defect

Case 1

Case 2

Pathological Specimens

Maude Abbott Medical Museum